Spinal cord injury (SCI) is thought to result in rapid and severe osteoporosis and is considered to be a common cause of disuse atrophy of bone. This condition predisposes the spinal cord injured patient to the risk of fracture and additional disability. The evolution and natural course of bone resorption following SCI, however, is poorly understood and has not been well described. A biochemical assay for urinary cross-linked N-telopeptides (NTx) of type I collagen has recently been developed and has been shown to be a specific and responsive marker for bone resorption activity (Eyre, 1995). To our knowledge, this assay has not been previously applied to the SCI population. In this pilot study, the NTx assay will be used, in a prospective manner, to characterize the biochemical profile of bone resorption in a group of acute (Group 1, n=10) and chronic (Group 2, n=10, > 6 months post injury) post-traumatic SCI patients. These two groups will each be compared with yoked controls, consisting of individual groups of age-matched uninjured subjects (Group 3, n=10 and Group 4, n=10). Analysis of variance will be used to identify any significant differences in NTx activity between groups and within each group over time. Alkaline phosphatase will be measured as a marker of bone formation at all time points in both experimental and control groups. The goals of the study are to measure NTx activity in normal controls and in patients with acute and chronic SCI over time in order to develop a clinically useful system to monitor the progression of osteoporosis following SCI.